In offshore activities, such as the exploration and production of offshore petroleum reserves, it is sometimes necessary to use offshore platforms as a base to perform these activities. Generally these platforms have a portable or fixed structure with vertically extending support legs. To service these offshore platforms, it is necessary to use vessels such as supply boats and barges, and to dock these vessels adjacent to the platforms to offload equipment and supplies. The problem of protecting these offshore structures from damage caused by collision between these vessels and the offshore structures is critical.
To protect these platforms, numerous prior art bumper systems have been designed and used. One protection system is know in the industry as the Lawrence Allison system. This system utilizes rubber tires mounted on a vertical support column positioned next to the platform leg. Some of these systems have the tires exposed and others surround the tires with a protective metal can.
Other prior art systems include the one shown in the United States Patent to Pogonowski U.S. Pat. No. 3,564,858, issued Feb. 23, 1971. This patent discloses boat landing systems for offshore structures in which a frame is supported from the legs of the platform. A spring support is provided on the upper end and on the lower end, a circular snubber or cuff of resilient material is used in a mounting to permit limited movement of the frame both horizontally and arcuately.
Other systems, such as is disclosed in the patent to Files U.S. Pat. No. 4,005,672, issued Feb. 1, 1977, utilize a shock-absorbing element on the upper support. A bottom joint is disclosed formed by a resilient cylinder positioned between two cylindrical members to permit angular displacement at the bottom.
In addition the patent to Files, U.S. Pat. No. 4,109,474, issued Aug. 29, 1978, utilizes a plurality of rubber bumper rings with top and bottom mounted shock cells.
Although these bumper systems have been quite satisfactory in many applications, they have not proved entirely satisfactory where large impact loads must be absorbed to protect the platform. In the previous designs, resilient elements surrounding vertical posts were utilized to absorb energy. When these elements were made of a sufficient toughness to prevent their destruction by contact with vessels, the energy absorbing capacities was substantially diminished, and in some applications, was negligible. Various designs for rings with hollow portions were attempted to return the energy absorbing capacity to these rings. These designs have not proved entirely satisfactory.